The present invention relates to a drying screen for drying a paper making web in the drying phase of a paper machine and to a method for manufacturing a drying screen, wherein the drying screen is provided with plastic threads.
In the drying phase of a paper making machine, i.e., after having passed through the wet end, the paper web is dried by means of contact, i.e., convection heating in a temperature range of 100.degree. to 150.degree. C. The paper web accompanies a so-called drying screen which rotates around a plurality of cylinders. The drying screen must be temperature resistant and must also withstand mechanical stress, especially in fast-running paper machines.
Prior art drying screens comprise either spiral wires which are connected to one another or a woven fabric of plastic filaments. These prior art drying screens are permeable to water vapor.
A drawback of the prior art drying screens is that as a result of the uneven arrangement of the wire or the yarn, the paper web does not contact the drying screen evenly but only at certain locations or lines. As a result, undesired markings are placed on the finished paper, i.e., grid-like patterns or striped patterns as impressions from the drying screen. Moreover, a smooth, even surface reduces the movement of air in the border region between paper and drying screen. The less air that is carried along, the fewer are the problems arising in regard to the covering. Moreover, the production of these prior art drying screens is time-consuming and expensive.